1. Field of the Invention
The present invention relates to an apparatus for driving a display panel such as a plasma display panel (referred to as a “PDP”) or an electroluminescence display panel (referred to as a “ELDP”).
2. Description of the Related Art
In recent times, display devices (PDP or ELDP) are often used for a television set mounted on a wall (referred to as a “wall TV set”). In general, the PDP and ELDP include a number of capacitive light-emitting elements.
Referring to FIG. 1 of the accompanying drawings, a device having a PDP as a display panel is schematically illustrated.
In FIG. 1, the PDP 10 includes a number of row electrodes X1 to Xn and Y1 to Yn. One row electrode Xi and one row electrode Yi define a pair of row electrodes, which serve as one horizontal line of a screen (displayed image). The PDP 10 also includes a number of column electrode pairs Z1 to Zm that extend perpendicularly to the row electrodes Xi and Yi. One column electrode Zi defines one vertical line of the screen. A dielectric layer (not shown) and a discharge space (not shown) are provided between the neighboring column electrodes Zi. A discharge cell, which serves to form a pixel, is formed at every crossing of the row electrode Xi and Yi pairs and the column electrodes Zi.
Each discharge cell has two illumination conditions only. One condition is a light emitting condition. In this condition, electrical discharge occurs in the cell. The other condition is a non-emission condition. In this condition, electrical discharge does not occur. Accordingly, the discharge cell is only able to produce two levels of brightness, i.e., a least bright level (no emission) and a most bright level (emission). The discharge cells are the only light emission elements in the PDP 10.
However, if the PDP 10 is operated by a drive apparatus 100 using a subfield method, the PDP 10 can present many levels of brightness (gradation or half tone) in accordance with an input image signal. The subfield method converts the input image signal to a plurality of N-bit pixel data (each N-bit pixel data corresponds to each pixel of the input image signal), and divides a display period for one field. (frame) to N subfields (subframes) such that one field corresponds to one bit of the N-bit pixel data. The subfield method assigns the number of discharges to the subfields (i.e., determines how many times each subfield should discharge) in accordance with the weights given to the subfields. As a result, the subfields are selectively caused to discharge (emit light) on the basis of the input image signal. The total number of discharges occurring in the subfields creates the halftone brightness for the one field. Thus, the display device can present various brightness levels in accordance with the input image signal.
One of subfield methods to drive the PDP is a selective light-extinction addressing method.
The selective light-extinction addressing method will be briefly described with reference to FIG. 2 of the accompanying drawings. The PDP 10 and the drive apparatus 100 shown in FIG. 1 are used here. In order to create desired half tone brightness, the drive apparatus 100 applies drive pulses to the row and column electrodes Xi, Yi and Zi of the PDP 10 in one subfield, based on the timing chart shown in FIG. 2.
Firstly, the drive 100 simultaneously applies a negative reset pulse RPx to the row electrodes X1 to Xn and a positive reset pulse RPy to the row electrodes Y1 to Yn. This is called “simultaneous resetting process Rc”. In response to the reset pulses RPx and RPy, all discharge cells in the PDP 10 discharge for resetting. As a result, a certain amount of wall charge is equally formed in each of the discharge cells. Accordingly, all the discharge cells are initialized to a light-emitting condition.
Subsequently, the drive apparatus 100 converts the input image signal to, for example, 8-bit pixel data for each pixel. The drive apparatus 100 divides the 8-bit pixel data to eight portions, which correspond to eight digits of the 8-bit pixel data respectively, to obtain pixel data bits, and generates pixel data pulses having pulse voltages corresponding to logic levels of the pixel data bits. For example, when the pixel data bit has a value “1” (logic level “1”), the drive apparatus 100 generates a pixel data pulse having a high voltage. When the pixel data bit has a value “0” (logic level “0”), the drive apparatus 100 generates a pixel data pulse having a low voltage (zero volt). As shown in FIG. 2, the drive apparatus 100 applies a group of pixel data pulses DP11-1m, DP21-2m, DP31-3m, . . . , DPn1-nm successively to the column electrodes Z1 to Zm. Each group of pixel data pulses is applied to one horizontal line of the screen. The one screen has n horizontal lines and m vertical lines (FIG. 1), and the pixel data pulses DP11-DPnm are grouped to n groups for the n horizontal lines. The drive apparatus 100 then generates scanning pulses SP, as shown in FIG. 2, and applies successively the scanning pulses SP to the row electrodes Y1 to Yn when the drive apparatus 100 applies the above-mentioned pixel data pulse groups DP. This is a pixel data writing process Wc. As a result, the discharge cells located at crossing points of the scanning-pulse-applied row electrodes Yi and the high-voltage pixel-data-pulse-applied column electrodes Zi are only caused to discharge (selective light-extinction discharge or selective elimination discharge). Therefore, the wall charges remaining in these discharge cells are eliminated. The discharge cells, which are initialized to the light emitting condition in the simultaneous resetting process Rc, are shifted to a no light emitting condition. On the other hand, other discharge cells, to which the scanning pulse PS is applied and the low voltage pixel data pulse DP is applied, do not undergo the selective light-extinction discharge. Thus, these discharge cells remain in the light emitting condition as they are initialized in the simultaneous resetting process Rc.
The drive apparatus 100 repeatedly applies the sustaining pulses IPx of positive polarity to the row electrodes X1 to Xn as shown in FIG. 2. When the drive apparatus 100 does not apply the sustaining pulses IPx to the row electrodes X1 to Xn, the drive apparatus 100 repeatedly applies the sustaining pulses IPy of the positive polarity to the row electrodes Y1 to Yn. This process is referred to as “light emission sustaining process Ic”. In the light emission sustaining process Ic, those discharge cells in which the wall charge remains, i.e., the discharge cells in the light emitting condition, only discharge every time the sustaining pulses IPx and IPy are alternately applied (light-emission sustaining discharge). In other words, those discharge cells which are set to the light emitting condition in the pixel data writing process Wc are only caused to repeat the light emission by the light-emission sustaining discharge. How many times the light-emission sustaining discharge should be repeated is determined in accordance with the weight attached to the subfield concerned. Therefore, these discharge cells maintain the light emitting condition. How many times the sustaining pulses IPx and IPy are applied is previously determined, based on the weights of the respective subfields.
Then, the drive apparatus 100 applies light-extinction pulses EP to the row electrodes X1 to Xn, as shown in FIG. 2 (light extinction process E). As a result, all the discharge cells simultaneously discharge for light extinction, whereby the wall charge remaining in the discharge cells is eliminated.
By executing a series of the above described processes a plurality of times in each of the fields, the PDP 10 presents halftone brightness that corresponds to a total number of light-sustaining discharge caused in the processes Ic of all the subfields of the field concerned.
In the pixel data writing process Wc as shown in FIG. 2, the scanning pulses SP are sequentially applied to the row electrodes Y1 to Yn so that the pixel data is written into the discharge cells for each horizontal line of the screen. Since the light emitting elements (discharge cells) of the PDP 10 are the capacitive light emitting elements, charge/discharge is caused in each of the discharge cells in each horizontal line of the screen every time the scanning pulse SP is applied to that horizontal line. In addition, since the pixel data pulse DP is applied to one column electrode Z while the scanning pulse is applied, those discharge cells which belong to this column electrode Z (i.e., the discharge cells to which no pixel data should be written) should undergo the charging/discharging. Therefore, a considerable amount of electrical power is consumed when the pixel data writing process is performed.